Note: Descriptions are shown in the official language in which they were submitted.
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S P~CIFTCATION
B~ckaround of the Invention
The present invention relates generally to circuit
condition monitoring devices for use in electrical power
distribution systems, and in particular to a clamp mechanism for
clamping such devices to the various sized cables of such
systems.
Electrical power distribution systems typically require
the use of a variety of monitoring devices to facilitate the
detection and location of system malfunctions. Among such
devices are manual and automatic reset fault current indicators,
and voltage monitoring devices. These devices are typically
either mounted on a test point provided on a system component, or
clamped directly onto a cable of the system.
Clamp-on mounting devices typically include a housing
which contains the monitoring device, a circuit condition
indicator, and some form of clamping mechanism for mounting the
housing on a cable. Since power cables used in the industry are
routinely of various diameters, it is necessary that the clamping
mechanism accommodate a range of cable diameters.
In one prior clamp mechanism, which is described in
U.S. Patent No . 4,456,873 of the present inventor, a plurality of
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flexible metallic strips are combined to form a generally square-
shaped core for use with a circuit condition monitoring device.
One end of the core is fixedly positioned relative to the device
housing, and the opposite end is detachably engaged to the one
end. In use, the opposite end is displaced from the engagement,
allowing the core to be passed around a cable.
Another prior clamp mechanism, which is described in
U.S. Patent No. 4,646,006, also of the present inventor, includes
a pair of clamp members biased for engaging movement toward one
another. A compression member between the clamp members
ordinarily prevents engaging movement of the members. When
pressed against a cable, the compression member deforms to allow
the clamp members to move toward one another and encircle the
cable and clamp a monitoring device thereon.
The present invention is directed to a clamp mechanism
having a resilient core and a device housing having a cable
engaging surface wherein a spring extends between the core
portions on either side of the conductor to bias the conductor
into engagement with the engaging surface. The spring is slidably
attached at one end to a bridging element which allows the spring
to slide and thereby extend less in accommodating cables of
varying diameters. This enables the same clamp and spring to be
used for a wide range of cable diameters.
Accordingly, it is a general object of the present
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invention to provide a new and improved clamp mechanism for a
circuit monitoring device.
It is a more specific object of the present invention
to provide a clamp mechanism for clamping a circuit condition
monitoring device to the cable of a power distribution system
wherein the cable has a range of diameters.
Summary of the Invention
A clamping mechanism for mounting a circuit condition
monitoring device on electrical cables having a predetermined
range of diameters, comprising a housing for the monitoring
device having a cable engaging surface, a core member extending
from the housing and adapted to encircle a cable, the core member
having a first portion generally on one side of the cable and a
second portion generally on the other side of the cable, and a
bridge member having one end attached to the first portion of the
core at a first location, and its other end attached to the first
portion of the core at a second location between the first
location and said housing. Biasing means are attached at one end
to the bridge member and attached at the other end to the second
portion of the core for biasing the conductor into engagement
with the cable engaging surface, the attachment to the bridging
member comprising a sliding attachment allowing the one end of
the biasing means to slide generally between the first location
and the second location on the first portion of the core, the
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second portion of the core including a gap between the point of
attachment of the spring means and the housing for passing the
cable into the core between the biasing means and the cable
engaging surface, and the one end of the biasing means sliding on
the bridging member to accommodate the predetermined range of
cable diameters.
Brief Description of the Drawinas
The features of the present invention which are
believed to be novel are set forth with particularity in the
appended claims. The invention, together with the further
objects and advantages thereof, may best be understood by
reference to the following description taken in conjunction with
the accompanying drawings, in the several figures of which like
reference numerals identify like elements, and in which:
Figure 1 is a perspective view of a fault indicator
incorporating a clamping mechanism constructed in accordance with
the invention showing the mechanism clamped on a power cable.
Figure 2 is a side-elevational view partially in
section of the fault indicator of Figure 1.
Figure 3 is a front plan view of the fault indicator of
Figures 1 and 2.
Figures 4a, 4b and 4c are side elevational views of the
fault indicator of Figure 3 illustrating the manner in which the
clamping mechanism accommodates power cables of various
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diameters.
Figure 5 is a perspective view of a fault indicator
incorporating a clamping mechanism comprising an alternate
embodiment of the invention.
Figure 6 is a side-elevational view partially in
section of the fault indicator of Figure 5 prior to installation
on a power cable.
Figure 7 is a cross-sectional view of the fault
indicator of Figures 5 and 6 taken along line 7-7 of Figure 6.
Figures 8 is a side-elevational view of the fault
indicator of Figures 5-7 showing the clamping mechanism thereof
being installed on a cable.
Figures 9a-9c are side-elevational views of the fault
indicator of Figures 5-8 illustrating the manner in which the
clamping mechanism of the invention fits onto power cables of
various diameters.
Figure 10 is a front elevational view of the fault
indicator of Figures 5-9.
DescriDtion of the Preferred Embodiment
Referring to the Figures, and Figures 1-4 in
particular, a circuit monitoring device, in this case a fault
current indicator 10, is illustrated installed on an electrical
cable 12 of an electrical power distribution system. Fault
indicator 10 includes a rectangular housing 14 at the front face
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of which a cylindrical readout 16 displays the condition of the
circuit with an internal indicator flag 18 visible through a
window 20. Upon the occurrence of a fault, flag 18 rotates to
the position shown to provide a visual indication that current in
excess of a predetermined level has flowed in cable 12.
In order for the fault indicator 10 to accurately
respond to the occurrence of fault current in cable 12, it is
necessary that the device be firmly positioned adjacent the
cable. To this end, the fault indicator is provided with a clamp
mechanism 22 constructed in accordance with the invention. As
best seen in Figure 1, the clamp mechanism extends from the rear
wall 24 of housing 14 opposite cylindrical readout 16 and fixes
the device in close contact with the cable.
A core assembly 26 is utilized for attaching the
housing 14 to a monitored conductor such as cable 12 and for
deriving the necessary magnetic flux in sufficient concentration
for powering the circuitry of the circuit module. The core
assembly is preferably formed as a closed loop of generally
rectangular configuration so as to completely encircle cable 12,
and includes a pull ring 28 means by which the core can be opened
to facilitate installation on or removal of the fault indicator
from a monitored conductor.
The core assembly 26 is seen to consist of a plurality
of individual strips or laminations 30 (Figure 2) formed of
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oriented silicon steel arranged side-by-side in a generally
rectangular closed-loop configuration. The core assembly is
preferably encapsulated in a layer 32 of vinyl plastisol
insulating material. As best seen in Figure 2, the rectangular
configuration includes a generally rectilinear first or left side
portion 34, a generally rectilinear second or right side portion
36 opposed to first portion 34, a pair of generally rectilinear
third or bottom portion 38, and a generally rectilinear fourth or
top portion 40 opposed to third portion 38. The closed loop
consisting of side portions 34, 36, 38 and 40 includes a gap 28
at the junction of the second or right side portion 36 and the
third or bottom portion 38.
To maintain cable 12 in engagement with cable engaging
surface 24 and gap 28 closed, the core structure includes two
helical springs 42. One end of each spring is secured to the
second or right side portion 36 by a wire clip 44, which includes
an eyelet portion for engaging the hooked end of the spring, and
a stem portion which extends through the laminations 30. The
other hooked end of springs 42 engages a bridge member 46 secured
on one end to the bottom side portion 38 by a wire clamp 44, and
on the other end to the left side portion 34 by a wire clip 44,
of the magnetic core assembly 26.
Because the spring members can be stretched along their
linear axis, they will automatically adapt to encircle cables of
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differing diameters. In this regard, the ends of springs 42
transverse bridge member 46 as the cable size increases.
Accordingly, the clamp mechanism automatically adjusts to the
dimension of the particular cable encountered. This adaptation
is best illustrated in Figures 4a-c where the position of the end
of the spring 42 on bridge member 46 is seen to be dependent on
the diameter of the cable.
The bridge member, which is inclined at a 45~ angle
relative to the cable engaging surface of the housing, enables
the spring to retain its resilient properties as the diameter of
the cable increases. If the spring was fixed at both ends, a
large cable would tend to overstretch the spring and cause it to
exceed its elastic modulus. Failure of the spring reduces the
mechanical integrity of the clamp assembly.
Instead, with the accommodation of the invention, the
bridge member provides a movable anchor at one end of the spring
which enables that end of the spring to move as the diameter of
the cables change. This allows the spring to extend less than
would otherwise be the case.
In an alternate embodiment of the invention, depicted
in Figures 5-10, the clamping mechanism of the present invention
utilizes a single spring and a single bridging element.
Referring to the figures, a circuit monitoring device, in this
case a fault current indicator 50, is illustrated in its normal
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operating position on an electrical cable 52 of an electrical
power distribution system. Fault indicator 50 includes a
rectangular housing 54 at the front face of which a cylindrical
portion 56 (Figure 10) contains a readout of condition. An
indicator flag 58 is visible through a window 60 provided in the
cylindrical readout portion 56 of the housing. Upon the
occurrence of a fault, indicator flag 58 rotates to a position to
provide a visual indication that a fault current has occurred in
cable 52. After such an event the fault indicator 50 may be
manually reset by depressing a reset button 62.
In order for the fault indicator 50 to accurately
respond to the occurrence of fault current in cable 52, it is
necessary that the cable firmly engage the cable engaging surface
of the fault indicator. To this end, the fault indicator is
provided with a clamp mechanism 64 constructed in accordance with
the invention. As best seen in Figure 5, the clamp mechanism is
attached to the cable engaging surface 66 of housing 54 opposite
the cylindrical readout portion 56.
A core assembly 68 is preferably formed as a closed
loop of generally rectangular configuration which completely
encircles cable 52. The core includes a gap 72 within a recess
70 in housing 54 to enable the core to be opened to facilitate
installation or removal of a monitored electrical conductor.
The core assembly 68 is seen to consist of a plurality
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of individual strips or laminations 74 (Figure 6) formed of
oriented silicon steel arranged side-by-side in a generally
rectangular closed-loop configuration and is preferably
encapsulated in a layer 76 of vinyl plastisol insulating
material. The rectangular configuration includes a generally
rectilinear first or left side portion 78, a generally
rectilinear second or right side portion 80 opposed to first
portion 78, and a generally rectilinear third or top portion 82
opposed to the cable engaging surface 66 of housing 54.
To maintain cable 62 engaged with cable engaging
surface 66 and gap 72 closed clamp mechanism includes a helical
spring 84. One end of this spring is secured to the second or
right side portion 80 by a wire clip 86, which includes an eyelet
portion for engaging the hooked end of the spring, and a stem
portion which extends through the laminations 74. The other
hooked end of spring 84 engages a bridge member 88 secured at its
ends to the left side portion 78 by additional wire clips 86.
When indicator 50 is not installed on a cable, the helical spring
84 rests within a channel 90 provided in the cable engaging
surface 66 of housing 54.
Prior to installation on a conductor, clamp mechanism
64 is shown in Figure 6 with gap 72 closed. In order to mount
the clamp mechanism on a cable, wire handles 92 and 93 may be
provided to pull the end of the core away from recess 70. During
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installation of the fault indicator, cable 52 is passed through
gap 72 (Figure 8), and the wire handle 92 is once again used to
insert the end of the core into recess 70 whereby gap 72 is
closed and cable 52 is securely engaged to the cable engaging
surface 66 of housing 54.
As shown in Figures 9a-9c bridge member 88, which may
be formed with a rigid wire, includes a first segment 94
projecting generally perpendicular to core member 78 at a first
location, and a second segment 96, which extends from the end of
the first segment to a second location on the core, preferably at
a 45~ angle to cable receiving surface 66.
As shown in Figures 9a-9c, for cables 52 of increasing
diameter the end of spring 84 slides along portion 96 of bridge
member 88, from its bottom end toward its top end, with the
result that spring 84 accommodates cables of increasing diameters
without exceeding its elastic modulous, while maintaining the
cable in engagement with cable engaging surface 66.
It will be appreciated that while the clamp mechanism
of the invention has been shown in conjunction with fault
indicating devices, it may be used to advantage with other types
of circuit condition monitoring devices, such as voltage
indicators.
While particular embodiments of the invention have been
shown and described, it will be obvious to those skilled in the
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art that changes and modifications may be made therein without
departing from the invention in its broader aspects, and,
therefore, the aim in the appended claims is to cover all such
changes and modifications as fall within the true spirit and
scope of the invention.
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